The invention relates generally to data storage systems and, more particularly, to disk based data storage systems.
A disk drive is a data storage device that stores data in concentric tracks on a disk shaped medium. Data is written to or read from the medium by spinning the medium about a central axis while positioning a transducer near a target track of the medium. During a read operation, data is transferred from the target track to an attached host through the transducer. During a write operation, data is transferred in the opposite direction. When a request to perform a read or write operation is received, the disk drive must move the transducer from a current position to a position that is substantially centered on the target track before a data transfer can take place. A servo control loop is typically provided for controlling the motion of the transducer. The servo control loop uses servo information stored on the surface of the disk, and read by the transducer, as feedback information for controlling the motion of the transducer.
The servo information that is located on the surface of the data storage disk is typically written to the disk before the disk is installed into the disk drive. The servo information can include, among other things, servo burst information (e.g., ABCD bursts) for defining a centerline of each track on the disk and track address information (e.g., Gray code data) for identifying each track on the disk. A servo track writer (STW) is normally used for writing the servo information to the disk. A STW is a highly precise machine that is capable of writing servo information on the disk surface with a high degree of positional accuracy.
Modern hard disk drives typically utilize a plurality of data storage disks arranged in a vertical stack configuration having a common axis of rotation. For such a disk drive, servo information is typically written by the STW to all of the disk surfaces in the stack simultaneously so that a number of vertically aligned xe2x80x9ccylindersxe2x80x9d results, each cylinder including one track on each disk surface. After the servo information has been written to the disk surfaces by the STW, the disk stack is mounted within the disk drive housing along with the other components of the disk drive.
The transducer associated with a particular disk surface in a disk drive is mounted to one end of an actuator arm which supports the transducer near the disk surface. The other end of the actuator arm is coupled to a voice coil motor that is operative for imparting motion to the actuator arm, in response to a control signal, to move the transducer in a radial direction with respect to the associated disk surface. Mechanical xe2x80x9ccrash stopsxe2x80x9d are implemented at the inner and outer extremes of transducer movement to act as a buffer should the transducer move beyond a desired movement range. Traditionally, the positional tolerance of the crash stops has been used as a reference to determine where to write the servo information on the surface of the disks in a disk drive. However, the positional tolerance of these crash stops is often large and can be unpredictable. Consequently, the position of the outermost track can sometimes be farther out than it should be, thus increasing the likelihood that the transducer will enter the dubbed off area near the outer diameter (OD) of the disk. This situation can lead to reduced reliability in the disk drive.
Therefore, there is a need for a method and apparatus for writing servo information on a data storage disk that is capable of reducing the likelihood that a track will be written too close to the outer diameter (OD) of the disk. There is also a need for a method and apparatus for writing servo information on a data storage disk that is capable of enhancing the reliability of the disk drive.
The present invention relates to a method and apparatus for writing servo information to a data storage disk that is capable of increasing disk drive reliability. The method and apparatus uses information relating to the location of the outermost edge of a textured landing zone on the disk as a reference for writing servo information to the disk. Preferably, the location of the outermost edge of the textured landing zone is determined on a disk drive by a disk drive basis so that the location of the tracks within a disk drive will be tailored to the individual drive. In a disk drive using multiple disk surfaces, a worst-case edge position is preferably determined for all of the disk surfaces within the drive. This worst-case position is then used as a reference for writing servo information to all of the disk surfaces. In one approach, the innermost track on a disk surface is placed as near as possible to the outer edge of the textured landing zone (or the worst case edge in a stack arrangement) taking into consideration the associated head geometry. Thus, for a given number of tracks, the position of the outermost track on the formatted disk surface will be as far from the outer diameter (OD) of the disk as possible.
In a preferred embodiment of the invention, the location of the outer edge of the textured landing zone is determined by the servo track writer. A number of different techniques for determining the edge location are provided. Each of these techniques involves moving a transducer in a radial direction with respect to the corresponding disk surface and monitoring a signal generated by the transducer. In one approach, a transducer that is sensitive to the changing gap between the transducer and the disk surface (e.g., a magneto resistive head) is used to detect the edge of the texture landing zone. In another approach, information is written to the surface of the disk for use in detecting the edge of the landing zone. In yet another approach, a transducer that is sensitive to mechanical vibrations (e.g., a piezo-electric element) is used to detect physical contact between the transducer and the textured landing zone. When the edge of the landing zone is detected using any of these techniques, the STW records the present position of the transducer. This position is then used as an indication of the location of the outer edge of the landing zone. The servo information is then written to the disk surface using the edge location as a reference.